Metatranscriptomics or prokaryotic RNA-seq? Which should you choose?

Metatranscriptomics and prokaryotic RNA-seq are two distinct approaches used in transcriptomics research. They differ in their objectives, organismal scope, and data-analysis strategies. The key differences are outlined below:

1. Study objective

• Metatranscriptomics: This approach analyses gene expression in samples containing a mixture of organisms. Metatranscriptomics examines the complete RNA pool regardless of its origin, including bacteria, archaea, eukaryotes, and viruses. It therefore provides a comprehensive view of gene activity in microbial ecosystems such as the gut microbiome, soil, and aquatic environments.
• Prokaryotic RNA-seq: Focuses exclusively on prokaryotic organisms such as bacteria and archaea. RNA-seq is used in this context to investigate gene expression in a specific bacterium or group of bacteria, revealing which genes are active under defined environmental conditions.

2. Organismal scope

• Metatranscriptomics: Includes prokaryotes, eukaryotes, and often viruses. It provides a more holistic view of all organisms present in a sample.
• Prokaryotic RNA-seq: Limited to prokaryotic organisms, namely bacteria and archaea. Samples may originate from different environments, but all organisms analysed with this approach must be prokaryotic.

3. Sample preparation and analysis

• Metatranscriptomics: Requires a more complex analytical workflow because the sample contains RNA from multiple organisms. RNA reads must be distinguished and assigned to the appropriate taxa, for example by mapping them against organism-specific reference databases. Low-abundance transcripts may be difficult to detect in the presence of dominant organisms. Bioinformatics analysis in this case includes:
  • Transcript assembly;
  • Taxonomic annotation;
  • Alpha- and beta-diversity analysis; functional annotation:
  • GO, KEGG, eggNOG, CAZy, CARD, PHI, etc.;
  • Statistical analysis and differential expression analysis.
• Prokaryotic RNA-seq: Sample preparation is more targeted because RNA is analysed from a single organism or a defined group of prokaryotes. This narrower scope simplifies read assignment. The bioinformatics workflow for prokaryotic RNA-seq includes:
  • Gene expression analysis;
  • Differential expression analysis;
  • Functional annotation and enrichment analysis; sRNA prediction and annotation;
  • Transcript structure analysis.

4. Application

• Metatranscriptomics: Primarily used to investigate complex microbial communities in natural environments. It is suitable for microbiome studies involving communities such as the gut microbiota, aquatic ecosystems, and soil.
• Prokaryotic RNA-seq: Used to investigate gene function in individual prokaryotic organisms or defined groups of prokaryotes, for example in studies of pathogens, bioremediation, and other microbiological applications.

Summary

• Metatranscriptomics is an approach for analysing RNA from mixed populations of organisms, including prokaryotes, eukaryotes, and viruses. It requires advanced methods for distinguishing RNA molecules and assigning reads to the organisms of origin.
• Prokaryotic RNA-seq focuses on RNA from prokaryotic organisms only, making the workflow more targeted and less complex in terms of read assignment. Prokaryotic RNA-seq provides more detailed information about the transcriptome of a specific organism. Its advantages include:
  • Analysis of transcriptomic changes in complex microbial communities and discovery of potentially novel genes.
  • Characterisation of interactions between microbial communities and their host or environment.
  • Use of a comprehensive metatranscriptome analysis software suite to maximise information recovered from microbial community transcriptomes.
  • Use of current gene-function databases to obtain more accurate information on gene expression in microbial communities.